In a network virtualization environment, one of the more common applications deployed on hypervisors are 3-tier apps, in which a web-tier, a database-tier, and app-tier are on different L3 subnets. This requires IP packets traversing from one virtual machine (VM) in one subnet to another VM in another subnet to first arrive at a L3 router, then forwarded to the destination VM. This is true even if the destination VM is hosted on the same host machine as the originating VM. This generates unnecessary network traffic and causes higher latency and lower throughput, which significantly degrades the performance of the application running on the hypervisors. Generally speaking, this performance degradation occurs whenever any two VMs are two different IP subnets communicate with each other.
FIG. 1 illustrates a logical network 100 implemented over a network virtualization infrastructure, in which virtual machines (VMs) on different segments or subnets communicate through a shared router 110. As illustrated, VMs 121-129 are running on host machines 131-133, which are physical machines communicatively linked by a physical network 105.
The VMs are in different segments of the network. Specifically, the VMs 121-125 are in segment A of the network, the VMs 126-129 are in segment B of the network. VMs in same segments of the network are able to communicate with each other with link layer (L2) protocols, while VMs in different segments of the network cannot communicate with each other with link layer protocols and must communicate with each other through network layer (L3) routers or gateways. VMs that operate in different host machines communicate with each other through the network traffic in the physical network 105, whether they are in the same network segment or not.
The host machines 131-133 are running hypervisors that implement software switches, which allows VMs in a same segment within a same host machine to communicate with each other locally without going through the physical network 105. However, VMs that belong to different segments must go through a L3 router such as the shared router 110, which can only be reached behind the physical network. This is true even between VMs that are operating in the same host machine. For example, the traffic between the VM 125 and the VM 126 must go through the physical network 105 and the shared router 110 even though they are both operating on the host machine 132.
What is needed is a distributed router for forwarding L3 packets at every host that VMs can be run on. The distributed router should make it possible to forward data packets locally (i.e., at the originating hypervisor) such that there is exactly one hop between source VM and destination VM.